Why are security bugs hidden in the Chromium issue tracker?

We must balance a commitment to openness with a commitment to avoiding unnecessary risk for users of widely-used open source libraries.

Can you please un-hide old security bugs?

Our goal is to open security bugs to the public once the bug is fixed and the fix has been shipped to a majority of users. However, many vulnerabilities affect products besides Chromium, and we don’t want to put users of those products unnecessarily at risk by opening the bug before fixes for the other affected products have shipped.

Therefore, we publicly open all security bugs within approximately 14 weeks of the fix landing in the Chromium repository. The exception to this is in the event of the bug reporter or some other responsible party explicitly requesting anonymity or protection against disclosing other particularly sensitive data included in the vulnerability report (e.g. username and password pairs).

Can I get advance notice about security bugs?

Vendors of products based on Chromium, distributors of Operating Systems that bundle Chromium, and individuals and organizations that significantly contribute to fixing security bugs can be added to a list for earlier access to these bugs. You can email us at security@chromium.org to request to join the list if you meet the above criteria. In particular, vendors of anti-malware, IDS/IPS, vulnerability risk assessment, and similar products or services do not meet this bar.

Please note that the safest version of Chrome/Chromium is always the latest stable version — there is no good reason to wait to upgrade, so enterprise deployments should always track the latest stable release. When you do this, there is no need to further assess the risk of Chromium vulnerabilities: we strive to fix vulnerabilities quickly and release often.

Can I see these security bugs so that I can back-port the fixes to my downstream project?

Many developers of other projects use V8, Chromium, and sub-components of Chromium in their own projects. This is great! We are glad that Chromium and V8 suit your needs.

We want to open up fixed security bugs (as described in the previous answer), and will generally give downstream developers access sooner. However, please be aware that backporting security patches from recent versions to old versions cannot always work. (There are several reasons for this: The patch won't apply to old versions; the solution was to add or remove a feature or change an API; the issue may seem minor until it's too late; and so on.) We believe the latest stable versions of Chromium and V8 are the most stable and secure. We also believe that tracking the latest stable upstream is usually less work for greater benefit in the long run than backporting. We strongly recommend that you track the latest stable branches, and we support only the latest stable branch.

Are privacy issues considered security bugs?

Privacy bugs, such as leaking information from Incognito, fingerprinting, and bugs related to deleting browsing data are not considered under the security VRP. The Chrome Privacy team tracks them as functional bugs.

Are denial of service issues considered security bugs?

No. While they are an inconvenience, we treat them as stability issues rather than security vulnerabilities, and they are not considered under the security VRP. That said, if you find a reproducible crash, we still encourage you to report it. The severity guidelines outline the types of bugs that are considered security vulnerabilities in more detail.

Are XSS filter bypasses considered security bugs?

No. Chromium contains a reflected XSS filter (called XSSAuditor) that is a best-effort second line of defense against XSS flaws found in web sites. There are a number of infrequently occurring corner cases, however, that it will never be able to cover. We do not treat these as security bugs in Chromium because the underlying issue is in the web site itself.

Why aren't physically-local attacks in Chrome's threat model?

People sometimes report that they can compromise Chrome by installing a malicious DLL in a place where Chrome will load it, by hooking APIs (e.g. crbug.com/130284), or by otherwise altering the configuration of the PC.

We consider these attacks outside Chrome's threat model, because there is no way for Chrome (or any application) to defend against a malicious user who has managed to log into your computer as you, or who can run software with the privileges of your operating system user account. Such an attacker can modify executables and DLLs, change environment variables like PATH, change configuration files, read any data your user account owns, email it to themselves, and so on. Such an attacker has total control over your computer, and nothing Chrome can do would provide a serious guarantee of defense. This problem is not special to Chrome ­— all applications must trust the physically-local user.

There are a few things you can do to mitigate risks from people who have physical control over your computer, in certain circumstances.

To stop people from reading your data in cases of device theft or loss, use full disk encryption (FDE). FDE is a standard feature of most operating systems, including Windows Vista and later, Mac OS X Lion and later, and some distributions of Linux. (Some older versions of Mac OS X had partial disk encryption: they could encrypt the user’s home folder, which contains the bulk of a user’s sensitive data.) Some FDE systems allow you to use multiple sources of key material, such as the combination of both a password and a key file on a USB token. When available, you should use multiple sources of key material to achieve the strongest defense. Chrome OS encrypts users’ home directories.

If you share your computer with other people, take advantage of your operating system’s ability to manage multiple login accounts, and use a distinct account for each person. For guests, Chrome OS has a built-in Guest account for this purpose.

There is almost nothing you can do to mitigate risks when using a public computer.

Assume everything you do on a public computer will become, well, public. You have no control over the operating system or other software on the machine, and there is no reason to trust the integrity of it.

If you must use such a computer, consider using an incognito mode window, to avoid persisting credentials. This, however, provides no protection when the system is already compromised as above.

The reason the password is masked is only to prevent disclosure via "shoulder-surfing" (i.e. the passive viewing of your screen by nearby persons), not because it is a secret unknown to the browser. The browser knows the password at many layers, including JavaScript, developer tools, process memory, and so on. When you are physically local to the computer, and only when you are physically local to the computer, there are, and always will be, tools for extracting the password from any of these places.

Does entering JavaScript: URLs in the URL bar or running script in the developer tools mean there's an XSS vulnerability?

No. Chrome does not attempt to prevent the user from knowingly running script against loaded documents, either by entering script in the Developer Tools console or by typing a JavaScript: URI into the URL bar. Chrome and other browsers do undertake some efforts to prevent *paste* of script URLs in the URL bar (to limit social-engineering) but users are otherwise free to invoke script against pages using either the URL bar or the DevTools console.

Similarly, users may create bookmarks pointed at JavaScript URLs that will run on the currently-loaded page when the user clicks the bookmark; these are called bookmarklets.

Is Chrome's support for userinfo in HTTP URLs (e.g. http://user:password@example.com) considered a vulnerability?

Not at this time. Chrome supports HTTP and HTTPS URIs with username and password information embedded within them for compatibility with sites that require this feature. Notably, Chrome will suppress display of the username and password information after navigation in the URL box to limit the effectiveness of spoofing attacks that may try to mislead the user. For instance, navigating to http://trustedsite.com@evil.example.com will show an address of http://evil.example.com after the page loads.

Although Chrome developers could try to reduce the fingerprintability of the browser by taking away (e.g.) JavaScript APIs, doing so would not achieve the security goal for a few reasons: (a) we could not likely get the distinguishability below 33 bits; (b) reducing fingerprintability requires breaking many (or even most) useful web features; and (c) so few people would tolerate the breakage that it would likely be easier to distinguish people who use the fingerprint-defense configuration. (See "Anonymity Loves Company: Usability and the Network Effect" by Dingledine and Mathewson for more information.)

There is a pretty good analysis of in-browser fingerprinting vectors on this wiki page. Browser vectors aside, it's likely that the browser could be accurately fingerprinted entirely passively, without access to JavaScript or other web features or APIs, by its network traffic profile alone. (See e.g. Silence on the Wire by Michal Zalewski generally.)

Since we don't believe it's feasible to provide some mode of Chrome that can truly prevent passive fingerprinting, we will mark all related bugs and feature requests as WontFix.

Where are the security indicators located in the browser window?

The topmost portion of the browser window, consisting of the Omnibox (or Location Bar), navigation icons, menu icon, and other indicator icons, is sometimes called the browser chrome (not to be confused with the Chrome Browser itself). Actual security indicators can only appear in this section of the window. There can be no trustworthy security indicators elsewhere.

Furthermore, Chrome can only guarantee that it is correctly representing URLs and their origins at the end of all navigation. Quirks of URL parsing, HTTP redirection, and so on are not security concerns unless Chrome is misrepresenting a URL or origin after navigation has completed.

Browsers present a dilemma to the user since the output is a combination of information coming from both trustworthy sources (the browser itself) and untrustworthy sources (the web page), and the untrustworthy sources are allowed virtually unlimited control over graphicalpresentation. The only restriction on the page's presentation is that it is confined to the large rectangular area directly underneath the chrome, called the viewport. Things like hover text and URL preview(s), shown in the viewport, are entirely under the control of the web page itself. They have no guaranteed meaning, and function only as the page desires. This can be even more confusing when pages load content that looks like chrome. For example, many pages load images of locks, which look similar to the meaningful HTTPS lock in the Omnibox, but in fact do not convey any meaningful information about the transport security of that page.

When the browser needs to show trustworthy information, such as the bubble resulting from a click on the lock icon, it does so by making the bubble overlap chrome. In the case of the lock bubble, it is a small triangular bump in the border of the bubble that overlays the chrome. This visual detail can't be imitated by the page itself since the page is confined to the viewport.

Why does Chrome show a green lock, even if my HTTPS connection is being proxied?

Some types of software intercept HTTPS connections. Examples include anti-virus software, corporate network monitoring tools, and school censorship software. In order for the interception to work, you need to install a private trust anchor (root certificate) onto your computer. This may have happened when you installed your anti-virus software, or when your company's network administrator set up your computer. If that has occurred, your HTTPS connections can be viewed or modified by the software.

Since you have allowed the trust anchor to be installed onto your computer, Chrome assumes that you have consented to HTTPS interception. Anyone who can add a trust anchor to your computer can make other changes to your computer, too, including changing Chrome. (See the section on, "Why aren't physically-local attacks in Chrome's threat model?").

What are the security and privacy guarantees of Incognito mode?

In particular, please note that Incognito is not a “do not track” mode, and it does not hide aspects of your identity from web sites. Chrome does offer a Do Not Track option, distinct from Incognito mode: chrome://settings/search#privacy.

When in Incognito mode, Chrome does not store any new history, cookies, or other state in non-volatile storage. However, Incognito windows will be able to access some previously-stored state, such as browsing history.

Why can’t I select Proceed Anyway on some HTTPS error screens?

A key guarantee of HTTPS is that Chrome can be relatively certain that it is connecting to the true web server and not an impostor. Some sites request an even higher degree of protection for their users (i.e. you): they assert to Chrome (via Strict Transport Security — HSTS — or by other means) that any server authentication error should be fatal, and that Chrome must close the connection. If you encounter such a fatal error, it is likely that your network is under attack, or that there is a network misconfiguration that is indistinguishable from an attack.

The best thing you can do in this situation is to raise the issue to your network provider (or corporate IT department).

Chrome shows non-recoverable HTTPS errors only in cases where the true server has previously asked for this treatment, and when it can be relatively certain that the current server is not the true server.

How does key pinning interact with local proxies and filters?

To enable certificate chain validation, Chrome has access to two stores of trust anchors: certificates that are empowered as issuers. One trust anchor store is the system or public trust anchor store, and the other other is the local or private trust anchor store. The public store is provided as part of the operating system, and intended to authenticate public internet servers. The private store contains certificates installed by the user or the administrator of the client machine. Private intranet servers should authenticate themselves with certificates issued by a private trust anchor.

Chrome’s key pinning feature is a strong form of web site authentication that requires a web server’s certificate chain not only to be valid and to chain to a known-good trust anchor, but also that at least one of the public keys in the certificate chain is known to be valid for the particular site the user is visiting. This is a good defense against the risk that any trust anchor can authenticate any web site, even if not intended by the site owner: if an otherwise-valid chain does not include a known pinned key (“pin”), Chrome will reject it because it was not issued in accordance with the site operator’s expectations.

Chrome does not perform pin validation when the certificate chain chains up to a private trust anchor. A key result of this policy is that private trust anchors can be used to proxy (or MITM) connections, even to pinned sites. “Data loss prevention” appliances, firewalls, content filters, and malware can use this feature to defeat the protections of key pinning.

We deem this acceptable because the proxy or MITM can only be effective if the client machine has already been configured to trust the proxy’s issuing certificate — that is, the client is already under the control of the person who controls the proxy (e.g. the enterprise’s IT administrator). If the client does not trust the private trust anchor, the proxy’s attempt to mediate the connection will fail as it should.

Can I use EMET to help protect Chrome against attack on Microsoft Windows?

There are known compatibility problems between Microsoft's EMET anti-exploit toolkit and some versions of Chrome. These can prevent Chrome from running in some configurations. Moreover, the Chrome security team does not recommend the use of EMET with Chrome because its most important security benefits are redundant with or superseded by built-in attack mitigations within the browser. For users, the very marginal security benefit is not usually a good trade-off for the compatibility issues and performance degradation the toolkit can cause.

Why are some web platform features only available in HTTPS page-loads?

The full answer is here: we Prefer Secure Origins For Powerful New Features. In short, many web platform features give web origins access to sensitive new sources of information, or significant power over a user's experience with their computer/phone/watch/et c., or over their experience with it. We would therefore like to have some basis to believe the origin meets a minimum bar for security, that the sensitive information is transported over the Internet in an authetnicated and confidential way, and that users can make meaningful choices to trust or not trust a web origin.

Note that the reason we require secure origins for WebCrypto is slightly different: An application that uses WebCrypto is almost certainly using it to provide some kind of security guarantee (e.g. encrypted instant messages or email). However, unless the JavaScript was itself transported to the client securely, it cannot actually provide any guarantee. (After all, a MITM attacker could have modified the code, if it was not transported securely.)

Which origins are "secure"?

Secure origins are those that match at least one of the following (scheme, host, port) patterns:

(https, *, *)

(wss, *, *)

(*, localhost, *)

(*, 127/8, *)

(*, ::1/128, *)

(file, *, —)

(chrome-extension, *, —)

That is, secure origins are those that load resources either from the local machine (necessarily trusted) or over the network from a cryptographically-authenticated server.

What's the story with certificate revocation?

Chrome's primary mechanism for checking the revocation status of HTTPS certificates is CRLsets.

Stapled OCSP with the Must Staple option (hard-fail if a valid OCSP response is not stapled to the certificate) is a much better solution to the revocation problem than non-stapled OCSP. CAs and browsers are working toward that solution (see the Internet-Draft: http://tools.ietf.org/html/draft-hallambaker-tlssecuritypolicy-03).

Additionally, non-stapled OCSP poses a privacy problem: in order to check the status of a certificate, the client must query an OCSP responder for the status of the certificate, thus exposing a user's HTTPS browsing history to the responder (a third party).

Chrome performs online checking for Extended Validation certificates if it does not already have a non-expired CRLSet entry covering the domain. If Chrome does not get a response, it simply downgrades the security indicator to Domain Validated.

Why does the Password Manager ignore autocomplete='off' for password fields?

Ignoring autocomplete='off' for password fields allows the password manager to give more power to users to manage their credentials on websites. It is the security team's view that this is very important for user security by allowing users to have unique and more complex passwords for websites. As it was originally implemented, autocomplete='off' for password fields took control away from the user and gave control to the web site developer, which was also a violation of the priority of constituencies. For a longer discussion on this, see the mailing list announcement.

In its default mode, Chrome Sync uses your Google password to protect all the other passwords in the Chrome Password Manager.

In general, it is a bad idea to store the credential that protects an asset in the same place as the asset itself. An attacker who could temporarily compromise the Chrome Password Manager could, by stealing your Google password, obtain continuing access to all your passwords. Imagine you store your valuables in a safe, and you accidentally forget to close the safe. If a thief comes along, they might steal all of your valuables. That’s bad, but imagine if you had also left the combination to the safe inside as well. Now the bad guy has access to all of your valuables and all of your future valuables, too. The password manager is similar, except you probably would not even know if a bad guy accessed it.

To prevent this type of attack, Chrome Password Manager does not save the Google password for the account you sync with Chrome. If you have multiple Google accounts, the Chrome Password Manager will save the passwords for accounts other than the one you are syncing with.

Does the Password Manager store my passwords encrypted on disk?

Chrome generally tries to use the operating system's user storage mechanism wherever possible and stores them encrypted on disk, but it is platform specific:

On Windows, Chrome uses the Data Protection API (DPAPI) to bind your passwords to your user account and store them on disk encrypted with a key only accessible to processes running as the same logged on user.

On Mac OS X, Chrome previously stored credentials directly in the user's Keychain, but for technical reasons, it has switched to storing the credentials in "Login Data" in the Chrome users profile directory, but encrypted on disk with a key that is then stored in the user's Keychain. See https://crbug.com/466638 for a longer form explanation.

On Linux, passwords are currently stored in KWallet or Gnome Keyring, where available. If they are not available, Chrome stores the passwords unencrypted on disk. The Password Manager team is currently migrating this to a similar setup as on Mac, where credentials would instead be stored in an encrypted DB, and the password to that DB will be stored in KWallet or Gnome Keyring. You can follow this process at https://crbug.com/602624.

On iOS, passwords are currently stored directly in the iOS Keychain and referenced from the rest of the metadata stored in a separate DB. The plan there is to just store them in plain text in the DB, because iOS gives strong guarantees about only Chrome being able to access its storage. See https://crbug.com/520437 to follow this migration.

I found a phishing or malware site not blocked by Safe Browsing. Is this a security vulnerability?

Malicious sites not yet blocked by Safe Browsing can be reported via https://www.google.com/safebrowsing/report_phish/. Safe Browsing is primarily a blocklist of known-unsafe sites; the feature warns the user if they attempt to navigate to a site known to deliver phishing or malware content. You can learn more about this feature in these references:

In general, it is not considered a security bug if a given malicious site is not blocked by the Safe Browsing feature, unless the site is on the blocklist but is allowed to load anyway. For instance, if a site found a way to navigate through the blocking red warning page without user-interaction, that would be a security bug. A malicious site may exploit a security vulnerability (for instance, spoofing the URL in the Location bar)-- this would be tracked as a security vulnerability in the relevant feature, not Safe Browsing itself.